Rotary pumps

ABSTRACT

A constant delivery rotary pump includes a rotor which rotates in a pumping chamber formed in an inner member and which carries round with it a set of pumping elements engaging the wall of the chamber and moving radially with respect to the rotor to perform a pumping action. The inner member is mounted in an outer member for sliding movement parallel to the line of action of the resultant of the fluid pressure acting in the pumping chamber. The outer member is fixed with respect to the axis of rotation of the rotor. A spring resists movement of the inner member relative to the outer member due to said resultant, and damped control means is provided for controlling in dependence on the pump delivery pressure the position of the inner member in its sliding movement. The control means includes a pair of wedge elements which are mounted side by side on their bases in the outer member and each of which has an apex in engagement with an inclined cam surface on the exterior of the inner member. The spring causes the inner member to rotate the wedge elements on to their bases, whilst the pump delivery pressure is applied between the elements and tends to rotate them about the outer side edges of their bases thereby moving the inner member against the spring force to control the pump delivery pressure.

United States Patent Martin et a1.

[54] ROTARY PUMPS [72] Inventors: Kenneth C. Martin, Walderslade, Chatham; Michael D. Baxter; John F. Holmes, both of Strood, Rochester, all of England [73] Assignee: Hobourn-Eaton Manufacturing Company Limited, Rochester, Kent, England [22] Filed: July 17, 1970 [21] Appl. No.: 55,748

[30] Foreign ApplicationPriority Data July 21, 1969 Great Britain ..36,659/69 [52] US. Cl. ..418/26, 418/27, 418/31 [51] Int. Cl ..F0lc 21/16, F030 3/00, F04c 15/04 [58] Field of Search ..418/24-27, 31, 418/71, 160

[56] References Cited UNITED STATES PATENTS 3,456,593 7/1969 Rosaen ..418/26 2,949,081 8/1960 Deschamps ..418/26 2,451,279 10/1948 De Lancey ..418/26 2,433,484 12/1947 Roth ..418/26 2,600,633 6/1952 French ..418/27 2,929,329 3/1960 Wallace ..418/26 3,015,212 1/1962 Krafft et a1. ..418/26 1 Aug. 29, 1972 [57] ABSTRACT A constant delivery rotary pump includes a rotor which rotates in a pumping chamber formed in an inner member and which carries round with it a set of pumping elements engaging the wall of the chamber and moving radially with respect to the rotor to perform a pumping action. The inner member is mounted in an outer member for sliding movement parallel to the line of action of the resultant of the fluid pressure acting in the pumping chamber. The outer member is fixed with respect to the axis of rotation of the rotor. A spring resists movement of the inner member relative to the outer member due to said resultant, and damped control means is provided for controlling in dependence on the pump delivery pressure the position of the inner member in its sliding movement. The control means includes a pair of wedge elements which are mounted side by side on their bases in the outer member and each of which has an apex in en gagement with an inclined cam surface on the exterior of the inner member. The spring causes the inner member to rotate the wedge elements on to their bases, whilst the piunp delivery pressure is applied between the elements and tends to rotate them about the outer side edges of their bases thereby moving the inner member against the spring force to control the pump delivery pressure.

12 Claims, 6 Drawing Figures PATENTED 3.687.579

* FIG].

2 ill!!! 4 25 511)) 1,

FIGS Flag ROTARY PUMPS This invention relates to rotary pumps.

According to this invention there is provided a rotary pump comprising an inner member which provides a pumping chamber, a rotor mounted for rotation within the pumping chamber, a plurality of pumping elements which can move radially with respect to the rotor and which are carried round by the rotor during rotation of the rotor and engage the peripherally extending wall of the chamber to perform a pumping action, means affording an inlet to and an outlet from the pumping chamber which inlet and outlet open to the pumping chamber at opposite sides of the axis of rotation of the rotor, an outer member which is fixed with respect to the axis of rotation of the rotor and within which the inner member is mounted for guided sliding movement in directions defined by the line of action of the resultant of the fluid pressure acting on said wall of the inner member during operation of the pump, resilient means acting between the outer and inner members to oppose movement of the inner member relative to the outer member resulting from increased delivery pressure of the pump, and damping means arranged to damp said sliding movement of the inner member relative to the outer member.

According to a preferred feature of the invention, an enclosed space is formed between the inner and outer members which space is full of fluid and the inner and outer members respectively provide surfaces which cooperate to support the inner member for said guided sliding movement and the damping means comprises a restrictor interconnecting the parts of said space at opposite ends of the co-operating surfaces According to another preferred feature of the invention, the damping means includes stop means providing a stop which engages the inner member in opposition to the resilient means and which effectively advances behind and retreats in front of the inner member as the inner member is moved by an increase in the delivery pressure and the resilient means respectively, said stop being mounted in the outer member for guided movement transversely to the direction of said sliding movement of the inner member and engaging the inner member with a wedge action.

In one construction the stop comprises an element having a base resting against the outer member, which element is rotatable with respect to the outer member about a said edge of the base and which has an edge remote from the base, which edge is laterally offset from said edge of the base relative to the direction of said sliding movement of the inner member and engages an inclined surface of the inner member, the force of the resilient means urging the inner member to rotate said element on its base. In an alternative construction the stop comprises a roller which co-operates with an inclined surface of the inner member and/or an inclined surface of the outer member to provide said wedge action.

Two embodiments of the invention will now be described with reference to the accompanying drawings in which:

FIG. 1 is a cross-sectional view of a pump according to the invention, the inner member being in a position wherein no pressure fluid is delivered,

FIG. 2 is a view similar to FIG. I. but showing the inner member in its position for maximum delivery,

FIG. 3 is a cross-sectional view similar to FIGS. 1 and 2 but with the rotor inner member and certain other parts removed,

FIG. 4 is a fragmentary sectional view on the line 4-4 of FIG. 1, and FIGS. 5 and 6 are fragmentary sectional views illustrating the use of rollers for the purposes of the invention.

Referring to FIGS. 1 to 4 of the drawings and more particularly to FIGS. 3 and 4, the pump 10 has a stout end member 11 which has formed therein an inlet passage 12 and an outlet passage 13 for fluid. The passages 12 and 13 open to the forward face of the end member in ports 14 and 15 respectively. The end member also provides a bearing for a shaft 16 which projects beyond said forward face and carries a rotor 17 on its projecting end. The rotor is secured to the shaft 16 for rotation therewith by a cotter 18 extending diametrically through aligned drillings in the rotor and shaft. The rotor is generally annular and has four radial slots 19 (FIGS. 1 and 2) spaced evenly round the axis of the rotor and extending over the full axial length of the rotor. A vane 20 is sealingly disposed in each slot 19 and is free for radial sliding movement in the slot. Wide axially extending channels 21 are formed in the external surface of the rotor between the vanes. An annular inner member 22 encircles the rotor and has a cylindrical inner surface which is swept by the vanes as the rotor rotates. The vanes are held radially in contact with the inner member by two rings 23 (see FIG. 4) which are respectively disposed in recesses in the forward and rearward ends of the rotor and which engage the radially inner ends of the vanes. The rings can orbit and rotate freely within the recess. Rotation of the rotor in the direction of the arrow shown in FIG. 2 causes fluid to be drawn through port 14 into the pumping chamber between the inner and outer members and to be pumped out through port 15 in the wellknown manner.

The inner member 22 is encircled by an outer casing member 25. An end cap 26 (FIG. 4) is disposed against the forward side of the outer member and four screws 28 clamp the end-cap 26 and outer member 25 to the end member 11. The axial end faces of the rotor 17, vanes 20 and inner member 22 form seals with the surfaces of the end member 11 and end cap 26.

The inner member is linearly slidable along a diameter thereof within the outer member, guided by two axially extending ribs 30 on the external surface of the inner member and by a pin 31 (see FIG. 3) mounted in the forward face of the end member 11 and engaging in a radial slot (not shown) in the adjacent end surface of the inner member. The ribs 30 do not in this construction form a seal with the adjacent surface of the outer member but form restrictors with the said surfaces to impede the flow of fluid past the ribs. As will be best understood from FIG. 2, during rotation of the rotor, the pressure of fluid being pumped, operating in the pumping chambers, tends to move the inner member 22 radially in a direction such as to compress a spring 32 which is disposed in a bore in the outer member 25 and the inner end of which seat in a recess in the exterior of the inner member. The outer end of the spring 32 rests against a plug 33 which is screwed into the outer portion of the bore, and the pressure of the spring can be adjusted by means of a plug.

Diarnetrically opposite the spring 32, two wedge elements 34 are seated on their bases in a recess 35 formed in the bottom chamber 36 in the outer member 25. The elements 34 and recess 35 extend across the full axial width of the outer member and the end of the elements form seals with the end cap 26 and end member 11. The elements are recessed on their faces nearer each other. Pressure fluid from the outlet passage 13 can flow along a passage 44 (FIG. 3) in the end member 11 to a port 38 which opens to the space formed between the elements by their recesses, so as to tend to cause the elements to rotate away from each other about the outer side edges of their bases from the position shown in FIG. 2 towards that shown in FIG. 1. The faces 34a of the elements 34 adjacent the inner member 22 are inclined away from each other. The outer surface of member 22 adjacent the wedge elements has an outwardly facing channel therein whose sides 40 extend generally parallel to the inclined surfaces of the elementsThe elements are urged into their upright positions (shown in FIG. 2) by respective compression springs 37 which are disposed in bores against screwed plugs 38 in the bores.

Under normal running conditions, the inner member 22 and the wedge elements take up positions between the extreme positions shown in FIGS. 1 and 2. If for any reason, such as an increase in the rotor speed, the delivery pressure of the pump increases, the inner member 22 moves against the restraint of the spring 32, so that the eccentricity of the inner member relative to the rotor is reduced. This in turn reduces the compression ratio of the pump and consequently reduces the delivery pressure. Thus the pump in practice tends to deliver fluid at a constant pressure. The pressure can be adjusted by means of a plug 33 to adjust the force exerted by spring 32. Spring 32 holds the inner member in contact with the wedge elements.

The wedge elements 34 also serve as stops damping the movement of the inner member 22 and preventing the member from oscillating in response to the pressure pulses which occur during normal operation of the pump. The fluid pressure applied between the wedge elements urges them apart and the elements pivot, the tips of the elements remaining in contact with the outer surface of the inner member. If the delivery pressure fails relatively slowly, the movement of the inner member actuated by spring 32 causes the inclined cam surfaces 40 to rotate the elements towards each other into their upright positions assisted by springs 37. The cam surfaces 40 thus apply a turning movement to the wedge elements about the bottom outer edges of the latter. In operation, the space between the inner and outer members is full of fluid and a port 41 (see FIG. 3) in the end member 11 opens to this space and communicates through a passage 42 with the inlet passage 12 so that the pressure in the space is controlled. The fluid which thus surrounds the wedge elements damps the response of the wedge elements to rapid pulses in the delivery pressure.

The fluid in the chamber 36 between the ribs and the wedge elements is at a higher pressure than the inlet port pressure because of a degree of leakage of pressure fluid from between the wedge elements into chamber 36 and because of the restrictor effect of the ribs 30. The space between ribs 30 and port 41 is of course at substantially the pump inlet pressure.

By providing an appropriate height/base-width ratio for the wedge elements, it has been found possible to dispense with the springs 37.

In alternative constructions shown in FIGS. 5 and 6 the wedge elements may be replaced by rollers 45 rolling on surfaces of the inner member (FIG. 5) and the outer member (FIG. 6,) 6 which surfaces are inclined to the direction of sliding movement of the inner member. Any convenient linkage incorporating a clamping device may be connected between the inner and outer members to damp movement of the inner member, but the construction illustrated in FIGS. 1 to 4 has been found to give particularly satisfactory results.

The embodiments described and illustrated is a vane type pump but the invention is equally applicable to a roller-type pump. The profile of the inner surface of the inner ring may be in the form of a cam instead of circular We claim:

1. A rotary pump comprising an inner member which provides a pumping chamber, a rotor mounted for rotation within the pumping chamber, a plurality of pumping elements which can move radially with respect to the rotor and which are carried round the rotor during rotation and engage the peripherally extending wall chamber to perform a pumping action, means providing an inlet to and an outlet from the pumping chamber which inlet and outlet open to the pumping chamber at opposite sides of the axis of rotation of the rotor, an outer member which is fixed with respect to the axis of rotation of the rotor and within which the inner member is mounted for guided sliding movement in directions defined by the line of action of the resultant of the fluid pressures acting on said wall of the inner member during operation of the pump, resilient means acting between the outer and inner members to oppose movement of the inner member relative to the outer member resulting from increased delivery pressure of the pump, and control means for controlling the position of the inner member in dependence on the delivery pressure of the pump, said control means comprising an element which is guided for movement transversely to said sliding movement of the inner member, the inner member being loaded into engagement with said element and the inner member and the element having cam engagement with each other whereby movement of the inner member under the influence of said resilient means urges the element in one direction in its guided movement, and said element having the delivery pressure of the pump applied thereto to move the element in the opposite direction and, through said cam engagement, to move the inner member in opposition to the force applied thereto by the resilient means, the element having a base resting against the outer member, which element is rotatable with respect to the outer member about a side edge of the base and which has an edge remote from the base, which edge is laterally offset from said edge of the base relative to the direction of said sliding movement of the inner member and engages an inclined surface of the inner member to provide said cam engagement, the force of the resilient means urging the inner member to rotate said element on to its base.

2. A rotary pump comprising an inner member which provides a pumping chamber, a rotor mounted for rotation within the pumping chamber, a plurality of pumping elements which can move radially with respect to the rotor and which are carried round the rotor during rotation and engage the peripherally extending wall chamber to perform a pumping action, means providing an inlet to and an outlet from the pumping chamber which inlet and outlet open to the pumping chamber at opposite sides of the axis of rotation of the rotor, an outer member which is fixed with respect to the axis of rotation of the rotor and within which the inner member is mounted for guided sliding movement in directions defined by the line of action of the resultant of the fluid pressures acting on said wall of the inner member during operation of the pump, resilient means acting between the outer and inner members to oppose movement of the inner member relative to the outer member resulting from increased delivery pressure of the pump, and control means for controlling the position of the inner member in dependence on the delivery pressure of the pump, said control means comprising first and second elements which are similar to and operate in conjunction with each other and each of which is guided for movement transversely to said sliding movement of the inner member, the inner member being loaded into engagement with both of said elements and the inner member having cam engagement with both of said elements whereby movement of the inner member under the influence of said resilient means urges each of said elements in one direction in the guided movement thereof, and each of said elements having the delivery pressure of the pump applied thereto to move each of said elements in the opposite direction to said one direction and, through said cam engagement, to move the inner member in opposition to the force applied thereto by the resilient means, said first and second elements each having a base resting against the outer member and being rotatable with respect to the outer member and away from the other elements about a side edge of the base, each of the elements further having an edge which engages an inclined surface of the inner member to provide said cam engagement and which is laterally offset from said side edge of the base relative to the direction of said sliding movement of the inner member, the force of the resilient means urging the inner member to rotate the said elements on to their bases.

3. A rotary pump comprising an inner member which provides a pumping chamber, a rotor mounted for rotation within the pumping chamber, a plurality of pumping elements which can move radially with respect to the rotor and which are carried round the rotor during rotation and engage the peripherally extending wall chamber to perform a pumping action, means providing an inlet to and an outlet from the pumping chamber which inlet and outlet open to the pumping chamber at opposite sides of the axis of rotation of the rotor, an outer member which is fixed with respect to the axis of rotation of the rotor within which the inner member is mounted for guided sliding movement in directions defined by the inner member during operation of the pump, resilient means acting between the outer and inner members to oppose movement of the inner member relative to the outer member resulting from increased delivery pressure of the pump, and control means for controlling the position of the inner member in dependence on the delivery pressure of the pump,

said control means comprising first and second elements which are similar to and operate in conjunction with each other and each of which is guided for movement transversely to said sliding movement of the inner member, the inner member being loaded into engagement with both of said elements and the inner member having cam engagement with both of said elements whereby movement of the inner member under the influence of said resilient means urges each of said elements in one direction in the guided movement thereof, and each of said elements having the delivery pressure of the pump applied thereto to move each of said elements in the opposite direction to said one direction and, through said cam engagement, to move the inner member in opposition to the force applied thereto by the resilient means, said first and second elements comprising a pair of contra-moving rollers which cooperate with inclined surfaces of the inner member to provide said cam engagement.

4. A rotary pump comprising an inner member which provides a pumping chamber, a rotor mounted for rotation within the pumping chamber, a plurality of pumping elements which can move radially with respect to the rotor and which are carried round the rotor during rotation and engage the peripherally extending wall chamber to perform a pumping action, means providing an inlet to and an outlet from the pumping chamber which inlet and outlet open to the pumping chamber at opposite sides of the axis of rotation of the rotor, an outer member which is fixed with respect to the axis of rotation of rotation of the rotor and within which the inner member is mounted for guided sliding movement in directions defined by the line of action of the resultant of the fluid pressures acting on said wall of the inner member during operation of the pump, resilient means acting between the outer and inner members to oppose movement of the inner member relative to the outer member resulting from increased delivery pressure of the pump, and control means for controlling the position of the inner member in dependence on the delivery pressure of the pump, said control means comprising first and second elements which are similar to and operate in conjunction with each other and each of which is guided for movement transversely to said sliding movement of the inner member, the inner member being loaded into engagement with both of said elements and the inner member having cam engagement with both of said elements whereby movement of the inner member under the influence of said resilient means urges each of said elements in one direction in the guided movement thereof, and each of said elements having the delivery pressure of the pump applied thereto to move each of said elements in the opposite direction to said one direction and, through said cam engagement, to move the inner member in opposition chamber to perform a pumping action, means providing an inlet to and an outlet from the pumping chamber which inlet and outlet open to the pumping chamber at opposite sides of the axis of rotation of the rotor, an outer member which is fixed with respect to the axis of rotation of the rotor and within which the inner member is mounted for guided sliding movement in directions defined by the line of action of the resultant of the fluid pressures acting on said wall of the inner member during operation of the pump, resilient means acting between the outer and inner members to oppose movement of the inner member relative to the outer member resulting from increased delivery pressure of the pump, and control means for controlling the position of the inner member in dependence on the delivery pressure of the pump, said control means comprising first and second elements which are similar to and operate in conjunction with each other and each of which is guided for movement transversely to said sliding movement of the inner member, the inner member being loaded into engagement with both of said elements and the inner member having cam engagement with both of said elements whereby movement of the inner member under the influence of said resilient means urges each of said elements in one direction in the guided movement thereof, and each of said elements having the delivery pressure of the pump applied thereto to move each of said elements in the opposite direction to said one direction and, through said cam engagement, to move the inner member in opposition to the force applied thereto by the resilient means.

6. A pump as claimed in claim 5, wherein each of said first and second elements consists of a roller which cooperates with an inclined surface of the inner member to provide said cam engagement.

7. A pump as claimed in claim 5, wherein each of said first and second elements consists of a roller which cooperates with an inclined surface of the outer member to provide said cam engagement.

8. A pump as claimed in claim 5, wherein each of said first and second elements is acted on by a spring in a sense to move the elements to move the inner member to increase the pump delivery pressure.

9. A pump as claimed in claim 5, wherein the two elements move in opposite directions to each other under the influence of the delivery pressure of the pump and wherein a closed space is formed between the elements which space has fluid at the pump delivery pressure supplied thereto.

10. A pump as claimed in claim 9, wherein the two elements are mounted in a chamber which communicates through a restricted passage with the pump inlet.

ll. A pump as claimed in claim 10, wherein an enclosed space is formed between the inner and outer members which space communicates with said chamber and the pump inlet and wherein the inner and outer members respectively provide surfaces which cooperate to support the inner member for said guided sliding movement and wherein the restricted passage interconnects the parts of said space at opposite axial sides of the co-operating surfaces.

12. A pump as claimed in claim 11, wherein the restricted passage is constituted by a clearance between the cooperating surfaces provided by the inner and outer members. 

1. A rotary pump comprising an inner member which provides a pumping chamber, a rotor mounted for rotation within the pumping chamber, a plurality of pumping elements which can move radially with respect to the rotor and which are carried round the rotor during rotation and engage the peripherally extending wall chamber to perform a pumping action, means providing an inlet to and an outlet from the pumping chamber which inlet and outlet open to the pumping chamber at opposite sides of the axis of rotation of the rotor, an outer member which is fixed with respect to the axis of rotation of the rotor and within which the inner member is mounted for guided sliding movement in directions defined by the line of action of the resultant of the fluid pressures acting on said wall of the inner member during operation of the pump, resilient means acting between the outer and inner members to oppose movement of the inner member relative to the outer member resulting from increased delivery pressure of the pump, and control means for controlling the position of the inner member in dependence on the delivery pressure of the pump, said control means comprising an element which is guided for movement transversely to said sliding movement of the inner member, the inner member being loaded into engagement with said element and the inner member and the element having cam engagement with each other whereby movement of the inner member under the influence of said resilient means urges the element in one direction in its guided movement, and said element having the delivery pressure of the pump applied thereto to move the element in the opposite direction and, through said cam engagement, to move the inner member in opposition to the force applied thereto by the resilient means, the element having a base resting against the outer member, which element is rotatable with respect to the outer member about a side edge of the base and which has an edge remote from the base, which edge is laterally offset from said edge of the base relative to the direction of said sliding movement of the inner member and engages an inclined surface of the inner member to provide said cam engagement, the force of the resilient means urging the inner member to rotate said element on to its base.
 2. A rotary pump comprising an inner member which provides a pumping chamber, a rotor mounted for rotation within the pumping chamber, a plurality of pumping elements which can move radially with respect to the rotor and which are carried round the rotor during rotation and engage the peripherally extending wall chamber to perform a pumping action, means providing an inlet to and an outlet from the pumping chamber which inlet and outlet open to the pumping chamber at opposite sides of the axis of rotation of the rotor, an outer member which is fixed with respect to the axis of Rotation of the rotor and within which the inner member is mounted for guided sliding movement in directions defined by the line of action of the resultant of the fluid pressures acting on said wall of the inner member during operation of the pump, resilient means acting between the outer and inner members to oppose movement of the inner member relative to the outer member resulting from increased delivery pressure of the pump, and control means for controlling the position of the inner member in dependence on the delivery pressure of the pump, said control means comprising first and second elements which are similar to and operate in conjunction with each other and each of which is guided for movement transversely to said sliding movement of the inner member, the inner member being loaded into engagement with both of said elements and the inner member having cam engagement with both of said elements whereby movement of the inner member under the influence of said resilient means urges each of said elements in one direction in the guided movement thereof, and each of said elements having the delivery pressure of the pump applied thereto to move each of said elements in the opposite direction to said one direction and, through said cam engagement, to move the inner member in opposition to the force applied thereto by the resilient means, said first and second elements each having a base resting against the outer member and being rotatable with respect to the outer member and away from the other elements about a side edge of the base, each of the elements further having an edge which engages an inclined surface of the inner member to provide said cam engagement and which is laterally offset from said side edge of the base relative to the direction of said sliding movement of the inner member, the force of the resilient means urging the inner member to rotate the said elements on to their bases.
 3. A rotary pump comprising an inner member which provides a pumping chamber, a rotor mounted for rotation within the pumping chamber, a plurality of pumping elements which can move radially with respect to the rotor and which are carried round the rotor during rotation and engage the peripherally extending wall chamber to perform a pumping action, means providing an inlet to and an outlet from the pumping chamber which inlet and outlet open to the pumping chamber at opposite sides of the axis of rotation of the rotor, an outer member which is fixed with respect to the axis of rotation of the rotor within which the inner member is mounted for guided sliding movement in directions defined by the inner member during operation of the pump, resilient means acting between the outer and inner members to oppose movement of the inner member relative to the outer member resulting from increased delivery pressure of the pump, and control means for controlling the position of the inner member in dependence on the delivery pressure of the pump, said control means comprising first and second elements which are similar to and operate in conjunction with each other and each of which is guided for movement transversely to said sliding movement of the inner member, the inner member being loaded into engagement with both of said elements and the inner member having cam engagement with both of said elements whereby movement of the inner member under the influence of said resilient means urges each of said elements in one direction in the guided movement thereof, and each of said elements having the delivery pressure of the pump applied thereto to move each of said elements in the opposite direction to said one direction and, through said cam engagement, to move the inner member in opposition to the force applied thereto by the resilient means, said first and second elements comprising a pair of contra-moving rollers which cooperate with inclined surfaces of the inner member to provide said cam engagement.
 4. A rotary pump comprising an inner member which provides a pumping chamber, a rotor mounted for rotaTion within the pumping chamber, a plurality of pumping elements which can move radially with respect to the rotor and which are carried round the rotor during rotation and engage the peripherally extending wall chamber to perform a pumping action, means providing an inlet to and an outlet from the pumping chamber which inlet and outlet open to the pumping chamber at opposite sides of the axis of rotation of the rotor, an outer member which is fixed with respect to the axis of rotation of rotation of the rotor and within which the inner member is mounted for guided sliding movement in directions defined by the line of action of the resultant of the fluid pressures acting on said wall of the inner member during operation of the pump, resilient means acting between the outer and inner members to oppose movement of the inner member relative to the outer member resulting from increased delivery pressure of the pump, and control means for controlling the position of the inner member in dependence on the delivery pressure of the pump, said control means comprising first and second elements which are similar to and operate in conjunction with each other and each of which is guided for movement transversely to said sliding movement of the inner member, the inner member being loaded into engagement with both of said elements and the inner member having cam engagement with both of said elements whereby movement of the inner member under the influence of said resilient means urges each of said elements in one direction in the guided movement thereof, and each of said elements having the delivery pressure of the pump applied thereto to move each of said elements in the opposite direction to said one direction and, through said cam engagement, to move the inner member in opposition to the force applied thereto by the resilient means, said first and second elements comprising a pair of contra-moving rollers which cooperate with inclined surfaces of the outer member to provide said cam engagement.
 5. A rotary pump comprising an inner member which provides a pumping chamber, a rotor mounted for rotation within the pumping chamber, a plurality of pumping elements which can move radially with respect to the rotor and which are carried round the rotor during rotation and engage the peripherally extending wall chamber to perform a pumping action, means providing an inlet to and an outlet from the pumping chamber which inlet and outlet open to the pumping chamber at opposite sides of the axis of rotation of the rotor, an outer member which is fixed with respect to the axis of rotation of the rotor and within which the inner member is mounted for guided sliding movement in directions defined by the line of action of the resultant of the fluid pressures acting on said wall of the inner member during operation of the pump, resilient means acting between the outer and inner members to oppose movement of the inner member relative to the outer member resulting from increased delivery pressure of the pump, and control means for controlling the position of the inner member in dependence on the delivery pressure of the pump, said control means comprising first and second elements which are similar to and operate in conjunction with each other and each of which is guided for movement transversely to said sliding movement of the inner member, the inner member being loaded into engagement with both of said elements and the inner member having cam engagement with both of said elements whereby movement of the inner member under the influence of said resilient means urges each of said elements in one direction in the guided movement thereof, and each of said elements having the delivery pressure of the pump applied thereto to move each of said elements in the opposite direction to said one direction and, through said cam engagement, to move the inner member in opposition to the force applied thereto by the resilient means.
 6. A pump as claimed in claim 5, wherein each of said first and second elemEnts consists of a roller which cooperates with an inclined surface of the inner member to provide said cam engagement.
 7. A pump as claimed in claim 5, wherein each of said first and second elements consists of a roller which cooperates with an inclined surface of the outer member to provide said cam engagement.
 8. A pump as claimed in claim 5, wherein each of said first and second elements is acted on by a spring in a sense to move the elements to move the inner member to increase the pump delivery pressure.
 9. A pump as claimed in claim 5, wherein the two elements move in opposite directions to each other under the influence of the delivery pressure of the pump and wherein a closed space is formed between the elements which space has fluid at the pump delivery pressure supplied thereto.
 10. A pump as claimed in claim 9, wherein the two elements are mounted in a chamber which communicates through a restricted passage with the pump inlet.
 11. A pump as claimed in claim 10, wherein an enclosed space is formed between the inner and outer members which space communicates with said chamber and the pump inlet and wherein the inner and outer members respectively provide surfaces which co-operate to support the inner member for said guided sliding movement and wherein the restricted passage interconnects the parts of said space at opposite axial sides of the co-operating surfaces.
 12. A pump as claimed in claim 11, wherein the restricted passage is constituted by a clearance between the cooperating surfaces provided by the inner and outer members. 